1. Field of the Invention
The present invention relates to an apparatus for detecting a defect of a circuit pattern of a semiconductor substrate or a semiconductor package which has a fine circuit pattern, and a defect detecting system having the same, and more particularly, to an apparatus for detecting a defect of a circuit pattern which detects presence of a defect in the connection of the circuit pattern of a semiconductor package by measuring a return loss of the circuit pattern according to an input signal output from a resonator, and a defect detecting system having the same.
2. Description of the Related Art
A semiconductor package is formed by mounting a semiconductor device on a substrate where a circuit pattern is formed. The semiconductor package needs to protect the semiconductor device from external surroundings and enable stable transmission of electric signals to the outside. In the semiconductor package, to stably transmit the electric signals, there must be no defect in the circuit pattern formed on the substrate. If a defect exists in the circuit pattern, reliability of a product is lowered in actual use thereof.
Thus, detecting a defect in the circuit pattern connection of a semiconductor package is one of very important works. During a semiconductor packaging process, the detection of a defect in electric connection is carried out in a final test step before mass production of the substrate and the final step of a packaging process in which a semiconductor device is mounted on the substrate. A visual inspection method, a capacitance measurement method, and a resistance measurement method are widely used for the detection of a defect.
However, with an increase of the number of input/output ports of a semiconductor device, a pitch of the circuit pattern formed on the substrate decreases so that the width of a circuit pattern decreases and the size of a defect generated in the circuit pattern decreases as well. Thus, when a circuit pattern having a fine pitch is inspected, since a difference between a voltage detected from a circuit pattern where a defect is not present and a voltage a circuit pattern having a defect is very small, it is difficult to detect the defect in spite of the presence of a defect. Although a variety of methods to detect a defect in a fine circuit pattern are used as shown in FIG. 1, these methods have the followings problems.
First, in a capacitance measurement method, electric conductivity is measured by one-to-one matching a probe and an electrode of a circuit pattern. This method can be simply used, but measurement of discontinuity is difficult.
Second, a resistance measurement method has a demerit in that a detection time increases when a circuit is shorted.
Third, in a measurement method using an E-beam, a circuit pattern is charged with an electron beam and a defect is detected according to whether a leakage occurs. However, this method is disadvantageous because a cost of an equipment for the method is high.
As a method to solve the above problems, U.S. Pat. No. 6,111,414. discloses a detection method using a resonator. In the method, since a single probe is used, the principle of measurement is simple, measurement time and resolution are superior to other conventional methods and reliability thereof is high.
FIG. 2 shows a circuit pattern defect detecting apparatus 1 using a resonator disclosed in U.S. Pat. No. 6,111,414. A radio frequency (RF) resonator 11 is connected between a probe 12 and an RF power supply portion Vin. The probe 12 contacts one end portion of a circuit pattern 13. An interconnect 14 connecting ports is formed on the circuit pattern 13.
In a defect detection method using the circuit pattern defect detection apparatus 1, a resonator having a relatively high quality factor is used to measure an electrical connection state of multi-chip modules. The presence of a defect is detected by comparing magnitude of an output voltage VOUT signal obtained by making the probe 12 contact the circuit pattern 13 having no defect and applying a voltage thereto, and an output voltage VOUT signal obtained by making the probe 12 contact the circuit pattern 13 having a defect and applying a voltage thereto.
In the circuit pattern defect detection apparatus 1 using the RF resonator 11, a signal at a particular frequency is amplified using the resonator after the signal is output from an RE source (not shown). The frequency and magnitude of the output voltage VOUT varies according to additional loading generated as the circuit pattern is connected to the resonant circuit.
FIG. 3 is a view showing the shapes and types of circuit pattern defects which can be generated during manufacture of a substrate. FIG. 4 is a graph showing a frequency response according to the types of the circuit pattern defects of FIG. 3. In FIG. 3, (a) through (e) correspond to cases of a defect-free state, an open defect, a mouse bite defect, a near-short defect, and a short defect, respectively.
As shown in FIG. 4, the resonant frequency and the magnitude in a state of not being connected to the circuit pattern are ωPROBE. and Mp, respectively. When the probe is connected to the circuit pattern, the resonant frequency and the magnitude of the output voltage VOUT are moved to ωREF and Mp in the graph, respectively, by additional loading of the circuit pattern.
The resonant frequency and the magnitude of the output voltage VOUT have changed characteristic values according to the state of the circuit pattern such as the defect-free state, the open defect, and the short defect. For the open defect, the peak moves from ωREF to ωOPEN and the magnitude thereof is slightly decreased. For the short defect, the resonant frequency ωSHORT moves to the left on the graph and the amount of decrease of the magnitude MS is greater than that of the open defect.
Accordingly, the resonant frequency and the magnitude change according to the type of a circuit pattern. Thus, if the resonant frequency and the magnitude in a defect-free state are known, a resonant frequency and a magnitude of a certain circuit pattern are measured and compared with those in the defect-free state so that the presence and type of a defect can be detected.
In the above measurement method, in case of a fine circuit, the presence of a defect is well detected at a position of a near end of the circuit pattern where the probe contacts. However, the presence of a defect at a position of a far end of the circuit pattern separated away from the near end where the probe contacts, is difficult to be detected. Also, even if a defect is detected, since a difference in the frequency and magnitude of the detected output voltage VOUT when a defect exists and the detected output voltage VOUT when a defect does not exist is not great, an error in measurement may be generated.
FIGS. 5 and 6 are graphs showing a differential voltage characteristic of a frequency between a defect-free case and cases in which a 30% mouse bite exists at a near end and a far end.
As shown in FIG. 5, when a 30% mouse bite exists at a near end, a resonant frequency is about 830 MHz and a differential voltage is about 190 mV. Also, as shown in FIG. 6, when a 30% mouse bite exists at a far end, a resonant frequency is about 850 MHz and a differential voltage is about 12 mV, which is smaller than that of FIG. 5 so that a larger differential voltage is required to accurately detect a defect. Also, since it is difficult to detect a defect generated in the far end of the circuit pattern, reliability of the circuit pattern cannot be guaranteed.